The present invention relates to vacuum holders for holding articles by suction. The invention is particularly useful when embodied in a vacuum table for holding various articles, such as printed circuit boards and the like, during inspection or other processing, and the invention is therefore described below particularly with respect to this application.
Vacuum tables are widely used for holding various types of articles during inspection and/or further processing. Such tables include a plurality of suction openings formed in the upper surface of the vacuum table and leading to a suction chamber, such that the suction openings covered by the article placed on the table apply suction to hold the article onto the table. However, it is desirable to construct the vacuum tables of relatively large size so as to accommodate articles of different dimensions. In such cases, some of the suction openings will not be covered by the articles. This results not only in a wastage of suction, but also in a substantial increase in the noise level produced by the flow of air through the suction openings not covered by the article.
The same problem exists not only with respect to vacuum tables, but also with respect to other types of vacuum holders, e.g. conveyor devices for gripping and conveying articles to other locations.